FIG. 1 illustrates the topography of a typical cellular telecommunications network 10 (e.g., mobile phone network). The network 10 is geographically divided into a number of cells or sectors 12, which are typically contiguous and which together define the coverage area of the network 10. Each cell 12 is served by a base station 14, which includes one or more fixed/stationary transceivers and antennae 16 for wireless communications with a set of distributed mobile devices 18 (e.g., mobile phones, wireless PDA's, wireless devices with high-speed data transfer capabilities, “WiFi”-equipped computer terminals, and the like) that provide service to the network's users. The base stations 14 are in turn connected (either wirelessly or through land lines) to a mobile switching center (“MSC”) or radio network controller (“RNC”) 20, which serves a particular number of base stations depending on network capacity and configuration. The RNC 20 acts as the interface between the wireless/radio end of the network 10 and a public switched telephone network or other network(s) 22, including performing the signaling functions necessary to establish calls or other data transfer to and from the mobile devices 18.
Various methods exist for conducting wireless communications between the base stations 14 and mobile devices 18. One such method is the CDMA (code division multiple access) spread-spectrum multiplexing scheme, widely implemented in the United States under the “IS-95,” “IS-2000,” or other standards. While early systems were primarily configured for voice communications, technological improvements have enabled the development of “3-G” (third generation) networks, such as CDMA-based 1x-EVDO wireless networks (1x-EVDO is an implementation of the CDMA2000® “3-G” mobile telecommunications protocol/specification configured for the high-speed wireless transmission of both voice and non-voice data.) and similar wireless networks for both voice and high-speed packet data transfer. In a CDMA-based network, transmissions from the mobile devices 18 to the base stations 14 are across a single frequency bandwidth known as the reverse link 24, e.g., 1.25 MHz centered at a first designated frequency. Generally, each mobile device 18 is allocated the entire bandwidth all of the time, with the signals from individual mobile devices being differentiated from one another using an encoding scheme. Transmissions from the base stations 14 to the mobile devices 18 are across a similar frequency bandwidth (e.g., 1.25 MHz centered at a second designated frequency) known as the forward link 26. The forward and reverse links may each comprise a number of traffic channels and access or control channels, the former primarily for carrying data, and the latter primarily for carrying the control, synchronization, and other signals required for implementing CDMA communications.
In a CDMA network, the reverse link access and traffic channels share the same air interface resource, the reverse link rise over thermal (“RoT”). RoT is a ratio between the total power in the reverse link and the thermal noise power that is seen at the base station. High RoT causes mobile devices to transmit higher power to transfer the same amount of information over the traffic channels of the air interface. Additionally, High RoT increases the likelihood that mobile devices will need to retransmit access requests with greater power over the access channels to be recognized by the base station. In order to ensure proper CDMA operation within the wireless network, RoT is typically controlled within a certain target range, for example, between 3-5 dB.
To maintain RoT within the proper range, wireless networks are typically provided with some sort of RoT overload control. For example, one conventional overload control method used in circuit switched networks is to drop a certain number of existing voice calls to alleviate congestion. However, control by dropping calls impacts network service availability and user satisfaction.
Both reverse access channels and reverse traffic channels contribute to the RoT. However, the RoT contributions of the access channels are less controllable than those of the traffic channels because the access channels use a contention based or random access protocol, whereas the traffic channels are subject to system call administration, channel assignment and close-loop power control.
Typically, it is unpredictable whether the access channels or the traffic channels will contribute more to the RoT because it depends on the number of connected mobile devices as well as the type of connections. Accordingly, when high RoT is observed in the system, the system will either reduce traffic channel loading or reduce access channel loading. In conventional CDMA networks, these two control functions are independent of one another. For example, where many mobile devices attempt to access the network, the system will observe a surge in access activity and the access control will likely reduce the access amount, while the traffic channel control will not be triggered. This results in high access blockings, which can result in a delay in user access.